1. Field of the Invention
The present invention relates to a magnetic closure device, and more particularly to the combination of a first element containing a permanent magenet for providing a magnetic attracting action and a second element that is capable of being attracted by the first element, whereby the first and second elements may be coupled detachably. The device may be used to fasten a flap on a bag, handbag, and the like, or may provide the equivalent function of a button on clothing.
2. Description of the Prior Art
A device that makes use of the magnetic attraction of the permanent magnet and provides the functions as described above is known to the prior art, and such a device has various constructions which are also known. Typically, the construction that is known as making the most effective use of the magnetic action of the permanent magnet includes a first element that provides the magnetic attracting action and a second element that is capable of being attracted by the first element, wherein the first element includes a permanent magnet formed in a cylindrical shape having a center bore that provides a first polarity, a first ferromagnetic plate provided on the side of the first polarity and which optionally may have a first ferromagnetic rod extending therefrom, and a nonmagnetic covering which packages those parts as a unit, and wherein the second element includes a second ferromagnetic plate detachably attached to a second polarity of the permanent magnet and having a second ferromagnetic rod extending therefrom that disengageably engages the first ferromagnetic plate or optionally the rod thereof through the respective bores of the covering and permanent magnet. This construction is disclosed in Japanese Patent Application laid open No. 2 (1990)-105503 and U.S. Pat. No. 4,021,891, for example.
For the device of the type described above, some parts of the permanent magnet are exposed visibly from the outside, which is not desirable from the standpoint of its appearance. To avoid this, the permanent magnet is generally packaged in a covering that is formed from any nonmagnetic material such as brass in a thin cylindrical shape closed at the top.
It is noted, however, that the conventional device construction described above has one problem in forming the covering in a thin cylindrical shape closed at the top so as to incorporate the permanent magnet therein. When the permanent magnet is incorporated within such a covering, it creates a magnetic gap with regard to both the attracting side and the attracted side, thereby weakening the magnetic attracting force. In order to provide a strong magnetic attracting force in this case, it is necessary to provide a covering that is formed to be as thin as possible. If a covering is too thin, it might lose its mechanical strength. As the covering has the trade-offs between its mechanical strength and thickness, it must be formed to the thickness sufficient to ensure the mechanical strength. For this reason, the minimum thickness that can be achieved is limited to a certain value. It is also noted that the covering becomes larger as the device construction is larger, which imposes further limitations on forming the covering to as thin as possible without affecting its mechanical strength.